All-solid-state batteries, in which the liquid electrolyte has been replaced with a solid electrolyte, have attracted attention in recent years. In comparison with secondary batteries using a liquid electrolyte, all-solid-state batteries, which do not use a liquid electrolyte, demonstrate both high cycle durability and energy density without undergoing decomposition of the electrolyte caused by overcharging the battery.
An example of the structure of an all-solid-state battery may be composed of a structure in which a positive electrode current collector layer, a positive electrode active material layer, a solid electrolyte layer, a negative electrode active material layer, and a negative electrode current collector layer are laminated. In general, it is preferable, in order to improve the energy density and performance thereof, that an amount of active material in the all-solid-state battery is large; and that the thickness of the solid electrolyte layer is as thin as possible. In particular, if the thickness of the solid electrolyte layer is able to be reduced, a correspondingly larger amount of active material can be contained in the all-solid-state battery.
However, in the case of having reduced the thickness of the solid electrolyte layer, there is an increased likelihood, for example, of the formation of pinholes and the like in a portion of the solid electrolyte layer, depending on the production conditions and the like of the solid electrolyte layer. Thus, studies have been conducted on methods for producing a solid electrolyte layer that is able to inhibit the formation of pinholes and the like while reducing thickness.
Regarding the method for producing, as a solid electrolyte layer for an all-solid-state microbattery, a lithium phosphate layer by atomic layer deposition, Non-Patent Document 1 (Biquiong Wang, Jian Liu, Qian Sun, Ruying Li, Tsun-Kong Sham and Xueliang Sun, “Atomic layer deposition of lithium phosphates as solid-state electrolytes for all-solid-state”, Nanotechnology, 2014, Vol. 25, No. 50) discloses a technology for forming a lithium phosphate layer on a substrate by alternately switching the atmosphere surrounding the substrate between a first atmosphere, containing a first precursor in the form of trimethyl phosphate, and a second atmosphere, containing a second precursor in the form of lithium tert-butoxide.